1. Field of the Invention
This invention relates to a process for the preparation of carbonyl sulfide, which is useful as a raw material for the production of pesticides, pharmaceuticals and other chemicals, by reacting carbon monoxide with sulfur in the vapor phase.
2. Description of the Prior Art
Many proposals have been heretofore made to produce carbonyl sulfide with a high purity and at an enhanced yield. It is a recognition common to all of these proposals that, when the vapor phase reaction of sulfur with carbon monoxide is carried out at an elevated temperature, e.g., exceeding 510.degree. C., carbonyl sulfide is inevitably thermally decomposed thereby producing carbon dioxide and carbon disulfide, and thus, the vapor phase reaction of sulfur with carbon monoxide should be carried out at a temperature of not higher than 510.degree. C. and as low as practically possible. For example, German Auslegeschrift No. 1,222,024 discloses a process for preparing carbonyl sulfide of a high purity wherein carbon monoxide is reacted with sulfur in the vapor phase in the absence of a catalyst at a temperature of from 350.degree. to 510.degree. C. Several processes are also known wherein the vapor phase reaction of carbon monoxide with sulfur is effected in the presence of a catalyst at a moderate temperature, for example, in the presence of an aluminosilicate at a temperature of from 500.degree. to 900.degree. F., i.e., from 260.degree. to 483.degree. C. (U.S. Pat. No. 2,983,580); in the presence of a metal sulfide selected from Na.sub.2 S, K.sub.2 S, NiS, CrS, CoS, WS and SnS at a temperature of 250.degree. to 450.degree. C. (U.S. Pat. No. 3,764,661); and in the presence of an alkaline earth metal compound at a temperature of from 250.degree. to 450.degree. C. (U.S. Pat. No. 4,078,045).
However, the above-mentioned process wherein the vapor phase reaction is carried out in the absence of a catalyst at a temperature of from 350.degree. to 510.degree. C. is not advantageous in that, first, the reaction rate is so low that a substantially long period is required for the completion of the reaction and thus a substantially large reactor is needed, and secondly, the reaction product contains a salient amount of unreacted carbon monoxide.
The above-mentioned processes wherein the vapor phase reaction is effected in the presence of a catalyst are advantageous in that a reaction product of a high purity can be obtained at a relatively low reaction temperature and in a relatively short reaction time. These processes are, however, not completely satisfactory in that, first, the catalyst must be completely dehydrated prior to the use thereof, because water, if present, causes a side reaction of decomposing carbonyl sulfide into hydrogen sulfide and carbon dioxide; secondly, sulfur tends to be deposited onto the catalyst particles which deposition leads to reduction in the catalyst activity and to clogging of the catalyst bed; and thirdly, most of the conventional catalysts exhibits a relatively short catalyst life.